Stress concentration factors of cold-formed high strength steel tubular T-joints

Abstract

A test programme looking into the stress concentration factors (SCF) of cold-formed high strength steel (CFHSS) traditional (without brace and/or chord rotation) and member-rotated tubular T-joints is described in this paper. The brace members of traditional T-joints were made of square, rectangular and circular hollow sections (SHS, RHS and CHS), while the brace members of member-rotated T-joints were made of SHS and RHS. On the other hand, the chord members of traditional and member-rotated tubular T-joints were made of SHS. In this study, member-rotated T-joints, include brace-rotated (BR), square bird-beak (SBB) and diamond bird-beak (DBB) tubular T-joints. The tubular members were cold-formed from thermomechanical control processed (TMCP) S900 and S960 steel grades plates. A total of 12 tests was conducted in this experimental investigation. An axial compression load was applied through the brace member, while the chord ends were supported on rollers. The brace and chord members of tubular T-joints were connected using the robotic gas metal arc welding process. The values of normal brace width-to-chord width ratio (β) ranged from 0.33 to 0.73, effective brace width-to-chord width ratio (β’) ranged from 0.40 to 0.87, brace thickness-to-chord thickness ratio (τ) ranged from 0.66 to 1.28 and chord width-to-chord thickness ratio (2γ) ranged from 20.6 to 39.0. The quadratic extrapolation method was used to estimate hot spot strains at the weld toes using the strains measured in the extrapolation regions. The experimental SCF values of CFHSS traditional and member-rotated tubular T-joints were compared with the SCF values obtained from the parametric equations given in the CIDECT (Zhao et al., 2001, [1]) and studies (Tong et al., 2013, [2]; Li et al., 2018, [3]; Tong et al., 2015, [4]). It was found that the existing SCF parametric equations given in the literature (Zhao et al., 2001, [1]; Tong et al., 2013, [2]; Li et al., 2018, [3]; Tong et al., 2015, [4]) could not accurately predict the SCF of cold-formed traditional and member-rotated tubular T-joints made of S900 and S960 steel grades.